Researchers pave the way for efficient large-scale organic solar cells with water treatment

Organic solar cells (OSCs) show many desirable properties, including high conversion efficiency and easy scalability. However, controlling the morphology of the active thin layer during uplift has proven to be challenging. In a new study, GIST researchers solve this problem by using deionized water as a method to control morphology, enabling highly efficient OSCs with large active regions. Credit: Dong-Yu Kim from Gwangju Institute of Science and Technology

Organic solar cells (OSCs), which use organic polymers to convert sunlight into electricity, have received significant attention for their desirable properties as next-generation energy sources. These properties include its light nature, flexibility, scalability, and high power conversion efficiency (>19%). There are currently several strategies to improve the performance and stability of OSCs. However, the problem remains the difficulty of controlling the morphology of the active layer in OSCs when scaling them to large areas. This makes it difficult to obtain high-quality thin films with an active layer, and thus adjust the efficiency of the device.

In a recent study, a team of researchers from the Gwangju Institute of Science and Technology in Korea set out to tackle this problem. In their work published in advanced functional materialsthey suggested a seemingly counterintuitive solution: the use of water treatment To control the morphology of the active layer.

Water is known to impede the performance of organic electronic devices, as it remains in ‘trap states’. Organic materials, which obstructs the flow of charge and degrades device performance. However, we found that using water instead of an active solution based on organic solvents as a processing method would enable the necessary physical changes to be made without causing chemical reactions,” explains Professor Dong Yu Kim, who led the study.

The researchers selected PTB7-Th and PM6 polymers as donor materials and PC61BM, EH-IDTBR and Y6 as acceptor materials for the active layer. They observed that vortex stimulation to mix the donor and acceptor materials in the active solution could result in an effective, well-mixed solution, however it was not sufficient on its own.

The active solution was hydrophobic, and accordingly, the researchers decided to use deionized (DI) water and vortexes to stir the solution. They allowed the donor and acceptor materials to sit in chlorobenzene (active host solution) overnight, then added DI water into the solution and stirred it, creating small swirls.

Due to the hydrophobic nature of the solution, the water pushed out the donor and acceptor molecules, causing them to dissolve more precisely in the solution. Then they let the solution rest, causing the water to separate from the solution. This water was then removed and the hydrotreated active solution was used to prepare thin films of PTB7-Th:PC61BM (F, fullerene), PTB7-Th:EH-IDTBR (NF, fullerene), and PM6:Y6 (H-NF, high-efficiency non-fullerene).

The researchers next examined the photoelectric performance of these thin films in the inverted hole-coated OSC formation and compared it with that of OSCs without water treatment.

“We noticed that the treated water was active solution Resulting in a more uniform active layer thin films, which showed higher energy conversion efficiency compared to those that were not treated with water. Furthermore, we manufactured large-area OSC units with an active area of ​​10cm2which showed a conversion efficiency of up to 11.92% for the hydrolyzed H-NF films”, says Professor Kim.

Efficiency over 14% for the triple active layer organic solar cell with a thickness of 300 nm

more information:
Nara Han et al., Introducing water treatment into slot-coated organic solar cells to improve device performance and stability, advanced functional materials (2022). DOI: 10.1002 / adfm.202204871

Provided by GIST (Gwangju Institute of Science and Technology)

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